Bending a geological icon: Oroclines, Pangea, and the supercontinent cycle

弯曲的地质标志：Oroclines、Pangea 和超大陆旋回

• 批准号: RGPIN-2014-06533
• 负责人: Johnston, Stephen
• 金额: $ 2.19万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=612285
• 关键词: Bending; geological; icon; Oroclines; Pangea

Pangea, the most recognizable of Earth Science icons, is the focus of my research. Wegener depicted Pangea as having formed in response to the Carboniferous continental collision of Gondwana in the south with Laurussia in the north giving rise to the Appalachian (in America) – Variscan (in Europe) Orogen. How one interprets the Appalachian - Variscan Orogen is dependent upon the nature of significant map-view bends that characterize both mountain belts. Are these map-view bends 'primary' paleogeographic features (promontories and recesses), or are they secondary 'oroclines' - formerly linear orogens that have been subsequently buckled about vertical axes of rotation? Most models assume the bends are primary structures, and imply that the final collision was preceded by an accretionary period during which 'peri-Gondwanan' continental ribbons (Avalonia; Meguma; South Portuguese Zone) that rifted from the north margin of Gondwana, opening the Rheic Ocean, collided with and accreted to the southern margin of Laurussia. Furthermore, Primary models imply that: 1 - peri-Gondwanan terranes are restricted to a belt bound by the Rheic suture to the south and the Laurussian autochthon to the north; 2 - multiple sutures characterize the southern margin of Laurussia, where they separate the peri-Gondwanan terranes, whereas a single Rheic suture bounds the north margin of the intact Gondwana passive margin; 3 - crustal thickening and orogenesis resulted from entry of the Gondwana passive margin into a subduction zone dipping beneath Laurussia; and 4 - post-collisional deformation of Pangea is explicable in terms of a within-plate, intra-continental tectonic setting. Support for an alternative model comes from our recent research of the Variscan Orogen in Iberia. Paleomagnetic, structural and stratigraphic studies demonstrate that the orogen is characterized by two coupled secondary oroclines that formed between 305 and 295 Ma, and which define a continental scale S-fold. Palinspastic restoration of the oroclines yields a 2300 km long previously linear NNE-striking orogen, and indicate that 1100 km of shortening at translation rates in excess of 10 cm/a was required to produce the oroclines. In our new model of the orogen, in which oroclinal buckling explains the map-view geometry of the orogen: 1 - peri-Gondwanan terranes (South Portuguese zone) lie east of the Rheic suture; 2 - Instead of being bound by a single Rheic suture, the Gondwana passive margin sequence forms a continental ribbon bound to the east by the Rheic suture, and to the west by a separate suture represented by ophiolite in NW Iberia; 3 – Variscan orogenesis is a product of subduction of the Gondwanan ribbon continent to the west beneath an oceanic arc, and not beneath Laurussia; and 4 - so-called post-collisional intra-Pangean orocline formation, which involved 1100 km of translation at rates of >10 cm/a, requires the involvement of subduction and hence the presence of oceanic lithosphere within the heart of Pangea well into the Permian. A program of geological, paleomagnetic, geochronological and geochemical studies focused along select transects across the Variscan orogen will test these contrasting models of Pangea construction. Expected outcomes include an improved understanding of Earth's paleogeography; better constraints on the relationship between Earth System evolution, including extinction events, and the supercontinent cycle; and an augmentation of outreach opportunities including public and school presentations.

盘古大陆是地球科学中最受认可的标志，韦格纳将盘古大陆描述为是由于南部冈瓦纳大陆与北部劳俄罗斯大陆碰撞而形成的，从而形成了阿巴拉契亚山脉（在美国）。瓦里坎（欧洲）造山带。人们如何解释阿巴拉契亚-瓦里坎造山带取决于代表这两个山脉的重要地图视图弯曲的性质。弯曲是“主要”古地理特征（海角和凹陷），还是次要“山坡”——以前是线性造山带，随后绕垂直旋转轴弯曲？大多数模型假设弯曲是主要结构，并暗示最终的碰撞是在此之前是一个增生期，在此期间，“近冈瓦纳”大陆带（阿瓦隆尼亚、梅古玛、南葡萄牙区）从冈瓦纳北缘裂开，打开此外，主要模型表明： 1 - 近冈瓦纳地体仅限于以南的瑞克缝合带和以北的劳俄罗斯本土为界的地带； - 多条缝合线是劳俄罗斯南缘的特征，它们将近冈瓦纳地体分开，而单一的瑞克缝合线则界定了北缘完整的冈瓦纳被动边缘；3 - 冈瓦纳被动边缘进入劳俄罗斯下方的俯冲带导致地壳增厚和造山作用；4 - 盘古大陆的碰撞后变形可以用板内大陆构造来解释对替代模型的支持来自我们最近对伊比利亚瓦里坎造山带的研究证明。该造山带的特征是在 305 Ma 和 295 Ma 之间形成的两个耦合的次生山坡，并且定义了山坡的大陆性 S 褶皱恢复，产生了 2300 公里长的先前线性 NNE 走向的造山带，并表明 1100 公里。在我们的造山带新模型中，需要以超过 10 厘米/年的平移速度缩短，其中口斜。屈曲解释了造山带的地图几何形状：1 - 近冈瓦纳地体（南葡萄牙地带）位于瑞克缝合线以东；2 - 冈瓦纳被动边缘层序形成了一条大陆带，而不是被单一的瑞克缝合线所束缚。东边是瑞克缝合带，西边是伊比利亚西北部蛇绿岩所代表的单独缝合带 3 – 瓦里斯坎造山作用是俯冲作用的产物；冈瓦纳带大陆向西在海洋弧下方，而不是在劳俄罗斯下方；4 - 所谓的碰撞后盘古大陆内山坡形成，涉及 1100 公里的平移，速度 > 10 厘米/年，需要俯冲作用，因此盘古大陆中心存在海洋岩石圈，深入二叠纪横跨瓦里斯造山带的横断面将测试盘古大陆构造的这些对比模型，包括更好地了解地球的古地理；更好地限制地球系统演化（包括灭绝事件）和超大陆循环之间的关系；公开和学校演示。